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DynamicPM option

The DynamicPM option shouldn't affect performance. It only switches to a low power mode during idle (DPMS active). When you are using the system, it switches back to the default power mode.

At the moment, this doesn't work for me. With activated DynamicPM option, the card always uses the lowest possible mode. But perhaps this isn't the right place for bug reports and of course it's still development code.

But nevertheless thank you for bringing power management to R700 based cards on linux! This saves nearly 17W for me in regular system operation, since the Radeon 4670 is only actually powersaving when those powerplay features are activated.

It's pretty cool that these things can be changed without crashing the GPU

This code only adjusts the engine clock so far, not the memory clock; changing engine speed is pretty safe because you can block acceleration while changing the clock. Changing the memory clock reliably is more difficult. You also need some pretty complex logic to make sure that the memory clock doesn't get too low for your display bandwidth and latency requirements, or you start to get artifacts on the screen very quickly.

Remember that dynamic power management is governed by Schmidt's law -- "if you mess with something enough, it'll break".

Note that this code probably needs to be moved into the drm if we want to have full activity-based power management. The X driver doesn't know about 3D driver activity, just 2D and video, but the drm knows about all the acceleration activity.

Originally Posted by Louise

How many pages would you say the final power management specs would be? 10 pages, 100 pages, 1000 pages ?

We'll probably try to identify a subset of the information which gives the biggest power savings without being too painful to code for on all the different GPUs and systems. As with 6xx 3D, we will probably release a mix of documentation and code.

Probably more than 10 pages but not a lot more, although if you count things like display bandwidth and latency calculations the numbers go up quickly.